1. Field of the Invention
The present invention relates to the field of semi-polar III-nitride films and materials and method for making the same.
2. Prior Art
Group III-nitrides, which include but are not limited to AlxInyGa1-x-yN compositions in which 0≦x, y≦1, are of considerable interest in many fields, such as the fabrication of high brightness light emitting diodes (LEDs), laser diodes, and power electronics. Virtually all group III-nitrides grown today are produced such that the maximum surface area available for device fabrication lies on the (00.1) c-plane, wherein the notation (hk.l) is a shorthand form of Miller-Bravais crystallographic notation to identify crystal planes in hexagonal crystals. The “.” Represents the i index in (hkil) four-index notation, which is redundant as h+k+i=0. One skilled in the art further understands that (hkil) notation using parentheses refers to a specific crystal plane while notation using curly brackets such as {hkil} refers to a family of related crystallographic planes. For the purposes of this invention, { } and ( ) notation will be understood to be interchangeable as the invention typically applies to all specific planes that belong to any family of planes.
Conventional c-plane-oriented nitrides can be referred to as “polar” nitrides because of the substantial piezoelectric and spontaneous polarization fields that exist parallel to the c-axis and therefore perpendicular to the c-plane. Such polarization fields restrict performance of polar group III-nitride devices by causing color shifting, limiting radiative recombination efficiency, and reducing high-current density efficiency.
An alternate set of group III-nitride crystal orientations are referred to as “semi-polar.” Semi-polar nitrides are nitride crystal planes having at least two non-zero h, k, or i indices and a non-zero l index in Miller-Bravais notation. Some common semi-polar planes include, but are not limited to, the {10.1}, {10.2}, {10.3}, {20.1}, {30.1}, and {11.2} planes.
Group III-nitrides are commonly fabricated by several techniques, including but not limited to metalorganic chemical vapor deposition (MOCVD or OMVPE), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE). The overwhelming majority of group III-nitride development has been focused on polar c-plane oriented material. Semi-polar group-III nitride planes, however, have historically proven difficult to grow by any technique using comparable parameters to polar nitrides. Indeed, one skilled in the art will recognize that growth of a semi-polar group-III nitride film, template, or free-standing layer using production parameters optimized for polar nitrides generally yields low-quality, rough, and defective material that is virtually unusable for fabrication of optoelectronic and electronic devices.